SF6 gas handling

Frequently Asked Questions

What are the most important quality criteria for SF6 gas in gas insulated switchgear (GIS)?

The following is of great importance: gas density, moisture concentration, decomposition products, gas purity (air concentration) which are determined by means of special SF6 measuring instruments as well as gas density controllers. DILO supplies all measuring devices required for these parameters.

Why is the SF6 quality in the GIS of great importance?

The gas quality is the decisive factor for the correct function of circuit breakers. Moisture or toxic and corrosive decomposition products in circuit breakers might have a negative impact on the insulation properties. 

When can SF6 be reused?

Reuse is allowed if the previous measuring results comply with the limit values stipulated in the IEC 60480 regulation (air, moisture and SO2 concentration). But essentially the indications of the switchgear manufacturers regarding the minimum quality of SF6 gas are to be followed. 

What is to be observed when working with SF6 gas?

In accordance with EC 517/2014 directive and implementing 2015/2066 regulation, only certified personnel is allowed to carry out the SF6 gas handling in Europe. 2015/2066 Regulation stipulates the minimum requirements for the certification of personnel.

DILO is an accredited authorisation company and is therefore allowed to hold training courses for the acquisition of the permission to carry out the recovery of SF6 gas.

What is the function of a service cart?

A service cart enables to recover the SF6 gas from a gas compartment to a final vacuum of < 1 mbar. Thereby the gas flows automatically via dry and particle filters which effectively adsorb decomposition products and moisture from the gas. During the gas recovery process the SF6 is stored either in gaseous or in liquid form. Furthermore, the air is evacuated from gas compartments. Afterwards, the gas compartments are refilled with SF6 to the desired operating pressure. The gas is led via filters and is purified once again while filling. 

What are the most important criteria when selecting a service cart?

The criteria are: volume of the gas compartment, filling pressure, gas volume to be stored, the desired time for the gas recovery, evacuation and filling processes as well as the final vacuum desired for the gas recovery process (< 5 or < 1 mbar). Our service cart selection tool allows for (pre-)selection of the eligible service carts, taking your particular requirements into account.

How can SF6 gas be stored?

SF6 can be stored in gaseous form, but under pressure and temperature in liquid form as well. This is carried out by means of compressors included in the SF6 maintenance devices. Thus, it is possible to store considerably higher gas quantities.

What is the final vacuum SF6 should be recovered to?

The IEC 62271-4 guideline stipulates a value of < 20 mbar. However DILO supplies SF6 maintenance equipment allowing a recovery of < 1 mbar.

When should the SF6 gas quality be measured?

The SF6 gas quality must be checked prior to the recovery of SF6 from gas compartments, in particular with regard to possible reuse in accordance with IEC 60480 directive. The key parameters here are moisture, decomposition products and gas purity. In general, the gas quality must always be checked if a decision regarding the reuse of the SF6 gas must be made or during the course of trend analysis for condition-based maintenance.

What must be done after having found contaminated gas in the circuit breaker?

In this case a prefilter unit should be connected between the gas compartment and the service cart which adsorbs most of the decomposition products and moisture. This is to avoid contamination of the SF6 service carts. 

How can the gas quantity in the circuit breaker be determined?

Since the introduction of the first EC 842/2006 and 1494/2007 directives on fluor gases, the SF6 gas quantity filled in the components must be indicated on the type plate. The SF6 gas quantity can also be recorded during gas recovery by means of a mass flow meter or bottle scales at liquid storage. In case of old SF6 filled components please get in contact with the manufacturer.

Why must electrical production equipment be evacuated prior to SF6 filling?

Before filling with SF6 gas the air and moisture must be evacuated from the gas compartment to a final vacuum of 1 mbar in order to prevent the SF6 gas from being mixed with air. 

When are N2/SF6 gas mixtures or CF4/SF6 gas mixtures used?

These mixtures are used to avoid liquefaction of the gas. When using gas mixtures to obtain the same puncture strength the gas pressure must be higher than when using pure SF6.

Which decomposition products may occur in case of failure in a GIS plant?

Toxic and corrosive decomposition products may occur. Corresponding measures for occupational health and safety in accoradance with local regulations which are in effect in your country are to be taken. For this purpose a special working protection kit has been compiled. 

Is it possible to separate SF6 by means of an SF6 maintenance device?

No it isn't possible. For this purpose special SF6/N2 separating plants are necessary. After the separating process the gas complies with the quality criteria for reuse stipulated in the IEC 60480 directive. However, DILO separating units allow the SF6 gas mixture to be purified to the extent that it even meets the standards of IEC 60376 directive (for new SF6 gas technical quality) with regard to moisture, SF6 percentage and decomposition products (SO2).

Which safety measures are to be taken if decomposition products are found in circuit breakers?

Please follow the local regulations for occupational health and safety which are in effect in your country. 

What must be observed for the transportation of SF6 maintenance devices containing SF6 gas?

In accordance with the ADR guidelines, SF6 may only be transported on roads under an exemption if the pressure of the gas in the maintenance unit or storage tank is a maximum of 2 bar at a temperature of 20 °C. At higher pressures, the transported material must be classified as a hazardous material and must be transported in suitable transport containers and labelled according to the actual gas quality in accordance with the ADR guidelines.

How can I reduce the pressure of a SF6 service cart to transport pressure?

In order to reach a transport pressure of max. 2 bar, a transport pressure reduction with pressure equalisation generally needs to be carried out in the device. Most DILO devices are equipped with a special control function which automatically establishes this pressure equalisation.

What is meant by SF6 monitoring?

Ultimately, this means the stock management of SF6 gas. The aim, ultimately, is to record all inflows and outflows of SF6 gas for the purposes of mass balancing.

How can I detect an SF6 leak?

Through a loss of pressure/density in the gas compartment.

How can I locate an SF6 leak?

By using a suitable leak indicator. The leak is located at the point where the highest concentration of SF6 is measured.